Many seeding and harvesting equipment are designed to be drawn behind tractors and the like. Most of these towed devices are steered primarily by the tractor and do not have their own steering mechanisms.
Under certain circumstances, however, it would be advantageous to be able to steer a towed implement independently from the tractor that is pulling it. For example, with seeding implements it is desirable for the seeding implement to remain aligned with the tractor at all times during seeding in order to obtain straight and even seed rows. However, often when a tractor is traversing in a direction perpendicular to the slope of the land, there is a tendency for the towed seeding implement to start “side slipping” or moving in the direction of the slope thereby falling out of alignment with the tractor. This results in uneven crop rows.
Another circumstance when it would be desirable to have an independently steerable implement would be where a tractor must manoeuvre the implement around an obstruction such as a slough, telephone pole, large boulder and the like. If the towed implement does not have independent steering, there is a tendency for the towed implement to “cut corners” thereby, in the case of a seeding implement, the seeding openers are moving sideways instead of straight ahead, which is the intended use.
Thus, a towed implement having independent steering would be able to steer itself back into alignment with the tractor. This can be accomplished by equipping the towed implements with at least one steerable surface engaging wheel, and more preferably, with two steerable surface engaging wheels attached to the rear of the main frame of the towed implement. Steering can either be automatically controlled by means of a turning sensor or could be operator controlled.
French Patent No. 2034151 (“'151”) teaches the use of ropes and pulleys to steer the rear wheels of a towed implement. In this instance, ropes are attached to the front hitch that connects the implement to the tractor and to two pivotally mounted wheels. When the angle of the front hitch strays from 90° relative to the front end of the main frame, the attached ropes are pulled in the direction of the hitch. The ropes, which are also attached to the rear wheels, will then pull the rear wheels to a degree corresponding to the angle of the hitch.
The system taught in '151 is undesirable for several reasons. First, the system would be constantly re-adjusting the angle of the rear wheels, resulting in the towed implement “wobbling” down the field. Second, if the side-hills on which the towed implement is being towed are particularly steep, the excess tension on the ropes could cause the ropes to break. Finally, there is no method for the operator to be able to control the amount the implement turns.